These aren't "bad" kids in the video. They don't intend to be mean or judgmental, and definitely not racist. They're just average kids, and most of them probably have great parents, just like Mikayla's. That's what makes the content of this video so shocking.
Personal note: I very sadly observed a 5-year-old act like this toward my 4-year-old daughter, who is black, not too long ago, and I watched his mortified dad fumble, unsure of what to do. Since then, we've come up with a few ideas. We can acknowledge we're not "post-racial," we can stop saying that we have a black president so there's no more racism, and we can affirm that this most certainly is a thing. Most importantly, we can talk to our kids, often and consistently, about race. Let's start with that and see where it takes us.